Syringe, having a rod and a piston and a disconnect mechanism

ABSTRACT

The invention relates to a disposable syringe which comprises a rod (5) that can be moved reciprocatingly in relation to a container (2). One end of the rod has the form of a needle (3), or can coact with a needle (3). The syringe also includes a piston (4) which coacts with the rod and which has means (6) for connecting the piston to the rod and disconnecting the piston therefrom. The rod (5) has an angled cross section and is provided with support and/or slide surfaces which coact with support and/or slide surfaces positioned peripherally on the piston (4).

TECHNICAL FIELD

The present invention relates to a syringe, and then particularly to adisposable syringe intended for one-time-use only.

The invention particularly pertains to the rod and the piston that formspart of the syringe and to the use of a special coupling or a specialmeans for controlling coaction between these syringe components.

The present invention relates to, or encompasses, a rod which forms partof a syringe intended for the injection of a liquid. A syringe of thiskind comprises a container a needle, a piston and the aforesaid rod, andalso a means for connecting and disconnecting the piston to and from therod.

Thus, the invention relates particularly to the configuration of the rodand to the configuration of a means which connects and disconnects therod to and from the piston, said rod being intended to form part of asyringe with which said means shall be brought to a connecting orcoupling state when the piston is initially withdrawn by the rod from aposition close to the needle to a position in which it is distanced fromthe needle, and is brought to a disconnected or uncoupled state when thepiston is urged forwards by the rod through an adapted, small distancein a direction towards the needle.

The invention constitutes a further development of a previously knownrod which forms part of a syringe intended for the injection of aliquid, wherein the rod is intended to coact with the container in amanner to twist the rod when it is moved in relation to the container,and wherein, in order to form said means, that part of the rod whichfaces towards the needle is provided with support surfaces which areintended to coact with opposing support surfaces on the piston.

The present invention also relates to, or encompasses, a piston whichforms part of a syringe intended for the injection of a liquid. Thissyringe is comprised of a container, a needle, the piston and a rod, andalso a means which functions to connect and disconnect the piston to andfrom the rod.

Thus, the invention relates particularly to the configuration of thepiston, and particularly to the configuration of the aforesaid pistonconnecting and piston disconnecting means intended to form part of asyringe in which said means is intended to be brought to a connecting orcoupling state when the piston is withdrawn by the rod from a positionin which it is located close to the needle to a position in which it isdistanced from said needle, and to be brought to a disconnected statewhen the piston is urged by the rod through an adapted, small distancein a direction towards the needle.

The invention constitutes a further development of a previously knownpiston which forms part of a syringe intended for the injection of aliquid, wherein the piston is intended to coact with the container in amanner such as to be moved rectilinearly when the piston is movedrelative to the container by a twistable rod, and wherein, for thepurpose of forming said connecting and disconnecting means, that part ofthe piston remote from the needle is provided with support surfaceswhich are intended to coact with opposing support surfaces on the rod.

BACKGROUND OF THE INVENTION

A disposable syringe for liquid injection on which the present inventioncan be said to be based is described in detail in the U.S. Pat. No.5,032,114, which illustrates a syringe of the kind described in theintroduction and with which the means which functions to connect anddisconnect the piston to and from the rod has a screw threadconfiguration. The embodiments of the rod disconnecting and connectingmeans described in this international patent application in FIGS. 6 and9 can be said to constitute the closest relevant prior art.

Other disposable injection syringes are also known to the art, forinstance the syringe described and illustrated in Swedish PatentPublication SE-B-79 02138-2, publication No. 438 598.

The injection syringe described and illustrated in the European PatentPublication EPA2-0 229 017 also forms part of the prior art.

Also forming part of the known art is the rod configuration described inpublication U.S. Pat. No. 5,004,460 and illustrated in FIG. 7 of saidpublication.

In addition to the aforecited publications, reference is also made tothe piston and rod coupling means illustrated and described in patentpublications U.S. Pat. No. 4,906,231, FR-A-2 381 527 and NO-A-163 263.

DISCLOSURE OF THE PRESENT INVENTION TECHNICAL PROBLEMS

When studying the earlier known art relating to disposable syringesintended for the injection of a liquid, it will be evident that atechnical problem resides in the providing conditions and a rodconfiguration which will enable the rod to be produced by plasticmolding techniques or like techniques to a degree of accuracy and amutual fit with the piston that will fulfill the requirement of goodfunctioning.

It will also be seen, particularly when taking into consideration theprior art taught by the aforesaid U.S. Pat. No. 5,032,114, that atechnical problem also resides in the provision of a rod provided withpiston connecting and disconnecting means which can be readilymanufactured in conjunction with the rod when manufacturing said rod byinjection molding in a plastic molding machine having a two-part die ormatrix.

It will also be seen that a technical problem resides in realizing alongwhich lines along the rod and the connecting and disconnecting meanssaid die parts shall coact, in order to enable and facilitate plasticmolding of the rod with said connecting and disconnecting means formedintegrally therewith, in a rational fashion.

When considering the aforesaid, it will also be seen that a technicalproblem resides in configuring or designing a rod terminating sectionpositioned adjacent the piston or the needle and to provide saiddisconnecting and connecting means with support surfaces and/or slidesurfaces and to realize that these surfaces should be inclined, withingiven limits, so as to achieve a satisfactory connecting anddisconnecting function between rod and piston.

It will also be seen that a further technical problem resides inrealizing how and within which angular values these surfaces should beinclined in order to ensure reliable disconnection of the rod from thepiston in response to a small, adapted twisting movement of the rod andsolely rectilinear movement of the piston.

Another technical problem which will be apparent from the aforegoingwithin the application recited is one of realizing the significance ofcoordinating a selected angle of inclination for the surfaces on the rodwith selected inclination of opposing surfaces on the piston.

Another technical problem is one of not only realizing the angularvalues that should be chosen, but also of providing connecting anddisconnecting means which are adapted and configured with view to themanufacturing technique used, said means having a short screw threadconfiguration with a pitch which conforms to but which is much smallerthan the pitch of the rod.

In order to achieve good functioning, another technical problem is oneof choosing the pitch of the screw thread configuration between supportand/or slide surfaces included in said means with a starting point fromselected rotation or twisting of the rod.

Another technical problem is one of realizing that when applying asimplified manufacturing technique for production of the rod in atwo-part die, it is necessary to assign the rod a very limitedrotational movement, or twisting movement, and therewith realize themaximum angular value permitted for this rotational movement.

Another technical problem is one of providing a rod of suchcross-section and of such configuration as to enable the rod to becomprised of thin plastic material but nevertheless exhibit sufficientflexural rigidity to ensure a positive function.

It will also be seen that a further technical problem resides inrealizing the significance of and the possibility associated withpermitting the rod, adjacent said connecting and disconnecting means, inthe form of a T-shaped rod terminating section, to present a disc-likemember formed integrally with the rod and serving as a guide against theinner wall of the container.

When considering the possibility of injection molding the rod,preferably from a thermoplastic material in a two-part die, it will beseen that when bearing in mind the desirability of affording sufficientrotation a further technical problem is one of realizing that thisrotation or twisting of the rod should be slightly smaller than 90°, andalso that the length of the support and/or slide surfaces forming saidconnecting and disconnecting means must be adapted so as to afford anaspiring path along which the rod and the piston can be moved backwardsand forwards through an adapted small distance, without loosing mutualcoaction, one with the other.

When considering the known prior art with regard to a disposable syringeintended for the injection of a liquid, it will be seen that a technicalproblem is one of providing conditions and a piston configuration, andalso the piston connecting and disconnecting means which will enable thesame to be produced by plastic molding techniques or the like, to adegree of accuracy and a mutual fit with the rod which will fulfill therequirement of good functioning.

It will then also be seen, particularly when considering the prior arttaught by the aforesaid U.S. Pat. No. 5,032,114, that a furthertechnical problem resides in the provision of a piston provided withpiston connecting and disconnecting means which can be manufacturedreadily in conjunction with the piston, when the piston is manufacturedby injection molding in a plastic molding machine in a two-part die.

When considering the aforesaid, it will also be seen that a technicalproblem resides in configuring or designing the piston and its sectionorientated from the piston or the needle so as to enable said connectingand disconnecting means to be produced in the form of support and/orslide surfaces on the piston, and to realize that at least some of thesesurfaces should be inclined within given limits in order to achievesatisfactory connecting and disconnecting function between rod andpiston.

In this regard, another technical problem is one of realizing how thesesurfaces should be inclined and within which angular values in order toensure that a positive and reliable disconnection will be obtainedbetween rod and piston when the rod is twisted or rotated through asmall angle and the piston moves only rectilinearly.

It will also be seen that a technical problem within the recited fieldof application is one of realizing the significance of coordinatingselected angles of inclination on the piston surfaces with selectedangles of inclination on the coacting rod surfaces.

In addition to realizing the values within which these angles ofinclination should be chosen, another technical problem is one ofproviding for said connecting and disconnecting means a suitableconfiguration which is adapted to the manufacturing technique used, thisconfiguration possibly including a short screw thread form with a pitchthat conforms to but which is much smaller than the pitch of the rod.

It will also be seen that another technical problem is one of providinga piston cross-section and a piston configuration which will enable thepiston to be manufactured from plastic material while exhibitingsufficient rigidity with regard to said connecting and disconnectingmeans, in the form of peripherally disposed and outwardly extending wallparts.

SOLUTION

The present invention relates to a disposable syringe and is based onthe known syringe described in the introduction and having the featuresset forth in claim 1.

The present invention therewith relates to a novel form of a rodintended to form part of a syringe intended for the injection of aliquid, and particularly to a disposable syringe of the kind whichcomprises a container, a needle, a piston and said rod and which alsoincludes means for connecting and disconnecting the piston to and fromthe rod, wherein said means is brought to a connecting or coupling statewhen the piston is withdrawn by the rod from a position in which it islocated close to the needle to a position in which it is distanced fromsaid needle, and is brought to a disconnecting or uncoupling state whenthe piston is urged by the rod through a small, adapted distance in adirection towards the needle, wherein the rod is intended to coact withthe container in a manner such that when the rod is displaced relativeto the container, said rod is twisted, or rotated, relative to thecontainer and the piston, and wherein the bottom part of the rod facingtowards the needle is provided with support and/or slide surfaces whichare intended to coact corresponding surfaces on the rod.

In accordance with the present invention, the rod of this earlier knownkind and forming part of a liquid injection syringe is permitted torotate, or twist, continuously along the whole of its length through anangle of not more than 90° or thereabouts, and in that the rod has anangled cross-section.

According to proposed embodiments, the rod has an angled cross-sectionwith a thin, planar centre part and with at least oneflexural-strength-enhancing edge. Preferably, the cross-sectional shapeof said rod will exhibit two such edges which extend away from oneanother.

It is also proposed that the support and/or slide surfaces on the rodforming part of said connecting and disconnecting means are inclinedslightly in a direction conforming to the direction of movement of therod downwards towards the needle and are formed peripherally to aT-shaped rod terminating section.

Further embodiments of the invention also include the provision ofmutually opposed, peripheral piston support and/or slide surfaces atmutually the same angle of inclination or slope.

It is also suggested that the T-shaped rod-terminating section islocated adjacent an overlying disc-like member having a diameter whichis only slightly smaller than the inner diameter of the container.

Finally, it is also proposed that the support and/or slide surfaces arecomprised of two upper and two lower peripherally orientated surfaces.

The present invention also relates to a novel type of piston formingpart of a syringe intended for the injection of liquid, and thenparticularly to a disposable syringe, and is based on a syringe of thiskind which comprises a container, a needle, said piston and a rod, andfurther comprises means for connecting and disconnecting the piston toand from the rod, wherein said means are constructed to be brought to aconnecting state when the piston is withdrawn by the rod, in response toa twisting movement, from a position close to the needle to a positiondistanced from said needle, and is brought to a disconnecting state whenthe piston is moved by a twistable rod rectilinearly through a small,adapted distance in a direction towards the needle, wherein the rod isintended to coact with the container in a manner such that when movedaxially in relation to the container, the rod will twist or rotate inrelation to the container and piston, and wherein the bottom part of therod that faces towards the needle is provided with support and/or slidesurfaces perpendicular, or at least essentially perpendicular, to acentre line on the rod, said surfaces being intended to coact withcorresponding surfaces on the piston.

According to the present invention, this earlier known liquid injectionsyringe is improved by inclining the support and/or slide surfaces onthe piston in a direction relating to the movement direction of the rod,said surfaces being formed peripherally in relation to the piston.

According to proposed embodiments which lie within the scope of theinventive concept, the opposed peripheral surfaces on the piston areformed in a peripheral wall section.

The slope or inclination shall preferably have the form of part of ascrew thread of restricted length along the periphery and having anangular value of less than 25°.

For the purpose of providing an aspiring function, it is also proposedthat the rod is able to move and rotate axially to a limited extent inrelation to the container and the piston, backwards and forwards,without the connecting and disconnecting means on the rod releasingtheir coacting contact with the piston connecting and disconnectingmeans.

ADVANTAGES

The advantages primarily afforded by the inventive disposable syringe isthat the rod is configured in a manner which will enable it to bemanufactured rationally from plastic components molded in a die ormatrix, and that the rod/piston connecting and disconnecting means havea configuration, or shape, which is adapted to said rational method ofmanufacture.

According to the invention, the main advantages afforded by a disposablesyringe and a piston included in a syringe intended for the injection ofa liquid are that the piston components, including the rod and pistonconnecting and disconnecting means have a shape or configurationsuitable for injection molding or light techniques.

The primarily characteristic features of an inventive syringe are setforth in the characterizing clause of claim 1.

The primary characteristic features of a rod forming part of a liquidinjection syringe in accordance with the present invention are set forthin the characterizing clause of claim 2.

The main characterizing features of a piston forming part of aninventive liquid injection syringe are set forth in the characterizingclause of claim 10.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplifying embodiment at present preferred and having featurescharacteristic of the present invention will now be described in moredetail with reference to the accompanying drawings, in which

FIG. 1A is a perspective, enlarged view of a section of a rod adaptedfor a container (not shown), and FIG. 1 shows support and/or slidesurfaces on said rod, arch, which are intended for coaction withcorresponding support and/or slide surfaces on a piston;

FIG. 2 is a perspective view of one-half of a two-part mold insert whichfunctions as a die for use when injection molding or die casting a rodand associated means;

FIG. 3A and 3B illustrate in side view and in enlarged scale a pistonhaving a groove in which the terminating end section of the rod isintended to fit, said groove functioning as a piston and rod connectingand disconnecting means;

FIG. 4 is a horizontal view of part of the piston, showing associatedsupport and/or slide surface and a complementary support and/or slidesurface on the rod;

FIGS. 5A through 5E illustrate the piston and rod connecting anddisconnecting means in different positions during part of a forwards andbackwards movement;

FIG. 6 illustrates in perspective the connecting and disconnecting meansof the piston and the rod respectively when said means are in engagementwith one another; and

FIGS. 7A through 7C illustrate different embodiments of the rodcross-section.

DESCRIPTION OF EMBODIMENTS AT PRESENT PREFERRED

Since the present invention is a direct development of the syringe andthe rod described and illustrated in the aforesaid U.S. Pat. No.5,032,114, reference is made to this publication, which is intended toconstitute part of the description of the present invention, in order toillustrate the function of a disposable syringe provided with rod andpiston connecting and disconnecting means.

Thus, FIG. 1 illustrates in perspective a rod-like element 5, which isadapted for insertion into a container 2 (not shown in FIG. 1) and thebottom part of which, i.e. the part facing towards a needle 3 (not shownin FIG. 1) is adapted for coaction with connecting and disconnectingmeans on a piston 4.

The present invention thus relates to a novel rod of novel constructionand novel configuration for inclusion in a disposable syringe 1 intendedfor the injection of liquid. This syringe comprises a container 2, aneedle 3, a piston 4 and the rod 5, and also means 6 which function toconnect and disconnect the piston to and from the rod.

The connecting and disconnecting means 6 are brought to a pistonconnecting position, or state, when the piston 4 is withdrawn by the rod5 from a position close to the needle 3 to a position where it isdistanced from the needle. The means 6 are brought to a disconnectingposition, or state, when the piston 4 is urged by the rod 5 through ashort, adapted distance in a direction towards the needle 3, wherein therod 5 is intended to coact with the container 2 in a manner such thatwhen moving relative to the container, the rod will be twisted, orrotated, in relation to the container 2 and the piston 4, which executesa rectilinear movement.

The part 5a of the rod 5 facing towards the needle 3 is provided withupper support surfaces 5k, 5m, which are perpendicular, or at leastgenerally perpendicular, to a rod centre line 5' and which are disposedto face upwards or away from the needle 3 and are intended to coact withoppositely located support surfaces on the piston 4.

The rod part 5a facing the needle 3 is also provided with bottom orlower support surfaces 5k', 5m', which are perpendicular, or at leastgenerally perpendicular, to a rod centre line 5' and which facedownwards or towards the needle 3, these support surfaces 5k', 5m' beingintended for coaction with oppositely located support surfaces on thepiston 4.

Depending on the construction chosen, the tolerances obtained and thechosen direction of movement, the aforesaid "support surfaces" will notonly function as piston support surfaces but also as slide surfacesacting between the respective connecting and disconnecting means on therod and the piston.

For example, it can be assumed that when moving the piston away from aposition close to the needle 3 to an upper position, the surfaces 5k, 5mwill function solely as support surfaces, but when the rod is moved upand down through a shorter distance in an aspiring function, thesurfaces will function both as support surfaces and as slide surfaces.

In particular, when the central, lowermost end surface of the rod 5 isprovided with a pressure surface 5a", in the form of a sphericalprojection or a circular plate of small extension, said surface 5a"being intended to press against a centrally located support surface onthe upper part of the piston, when the rod 5 urges the piston 4 towardsthe needle 3 and during the terminating movement, the aforesaid surfaces5k' and 5m' will primarily function as support surfaces which positionthe piston correctly and which are intended to support against theperiphery of the piston and therewith prevent the piston from tilting.

It has been found highly beneficial to slightly incline at least theupper surfaces 5k, 5m on the rod 5 in a direction conforming with thedirection of rotation of the rod, i.e. the direction of rotation inwhich the rod 5 is moved towards the needle 3, through an angle "a" andto give these surfaces e peripheral, inverse T-shape on the terminatingrod section 5a'.

The value of the angle "a" shall be smaller than 25°, preferably between5-15° in relation to a selected horizontal plane 5x. The bottom supportsurfaces 5k' and 5m' on the rod 5 may also be inclined slightlydownwards at an angle of "a'" and these surfaces are also formedperipherally on the rod terminating section 5a'.

The value of the angle "a'" will preferably be the same as that of theangle "a" in relation to a chosen horizontal plane 5x'.

The angular value of the rod, referenced "b" is between 70° and 80°.

The oppositely located surfaces on the piston have the same angle ofinclination as those on the rod.

As shown in FIG. 1, the rod 5 is intended to be twisted through anangle, which from the aspect of practical manufacture, must be slightlyless than 90°, and because the largest possible angle of rotation isdesired, it is proposed that the angle through which the rod can rotate,or twist, is at least greater than 80°.

Seen practically and when using a two-part die or mould, this angularvalue is preferably 88°-89°.

The rod has an angled cross-sectional shape and exhibits a broad centraland thin part 5p, having formed integral therewith stiffening edges 5r,5s, which extend away from one another and which are equally as thin assaid broad part 5p.

The T-shaped rod terminating section 5a' is located adjacent adisc-shaped member 5t whose diameter is only slightly smaller than theinner diameter of the container 2, said disc therewith forming means forguiding the bottom part of the rod in relation to the container.

By selecting the angles "a" and "b" in the manner aforesaid, anaspiration distance is provided by the angular difference of thetransverse extension of the support surfaces 5k, 5m and on the length ofthe oppositely located support surfaces on the piston, which enables therod to be moved reciprocatingly through an adapted, small distance inresponse to a small twisting movement, without the respective connectingand disconnecting means 6 relinquishing their mutual coaction when thepiston moves in a straight line.

The whole of the rod 5 is manufactured in one piece, among other things,with an integrated upper pressure plate 8.

FIG. 2 illustrates in perspective one-half of a two-part mold insertwhich functions as a die or mould, and further illustrates where aselected interface line or border between the die parts shall be placedin order to produce, in one working operation, the rod with saidintegrated, upper pressure plate, an adapted angle of rotation, a lowerdisc and said associated connecting and disconnecting means.

FIG. 3 is a side view of a circular piston 4 adapted for insertion intoa container 2 (not shown in FIG. 1) and the upper part of which, i.e.the part facing away from the needle 3 (not shown) is adapted forcoaction with connecting and disconnecting means on a rod.

Thus, the present invention relates to a piston of novel configurationand construction for use in a disposable syringe intended for theinjection of a liquid. The syringe is comprised of a container 2, aneedle 3, said piston 4, a rod 5 and means for connecting anddisconnecting the piston to the rod.

The part 5a of the rod 5 facing towards the needle 3 is also providedwith bottom support surfaces 5k', 5m' which extend perpendicularly or atleast essentially perpendicularly to a centre line on the rod and whichface downwardly or towards the needle 3, said support surfaces 5k', 5m',being intended to coact with oppositely located support surfaces 4k' and4m' respectively on the piston 4.

As shown in FIG. 3, the groove is intended to extend slightly upwardsand has parallel surfaces 4k and 4k'.

The value of the angle "c" shall be less than 25°, preferably between5°-15°.

The oppositely located support surfaces 4k, 4m on the piston 4 have thesame angle of inclination as the support surfaces 5k, 5m on the rod.

The surface extension of the rod and the piston support surfaces has theform of a screw thread or is flat and of very limited length.

The choice of the angle of inclination is significant in ensuring anecessary sliding action between rod and piston, so that the rod can betwisted without the piston taking part in the twisting movement.

The piston shall move in a straight line in the container.

In order to afford limited movement of the rod 5 up-and-down in relationto the container 2 while maintaining coaction with the piston 4, thereis provided the possibility of performing an aspiration function. Theconnecting and disconnecting means 5a' on the rod shall be able to slideand rotate relative to the connecting and disconnecting means on thepiston in the form of a groove, said piston following this limitedmovement rectilinearly.

The maximum permitted length of said movement distance while retainingsaid coaction will depend on the angle through which the rod is twisted,the length of the groove in the piston and its angle and the width ofthe T-shaped rod terminating section 5a'.

In practice, this movement distance should be from 2-5 mm.

It will be obvious that this limited axial movement of the rod 5 and thepiston 4 connected thereto, up-and-down in the container 2, will meanthat the means for connecting and disconnecting the piston to and fromthe rod will constantly have a connecting position. The aforesaid means6 are not brought to a disconnecting position until the rod 5 and thepiston 4 have moved beyond the distance of said limited movement towardsthe needle, in that the right edge of the support surface 5k on the rod,FIG. 3, moves out of engagement with the left edge of the support and/orslide surface 4k on the piston 4.

This is shown more clearly in FIG. 3 in a broken-line position, where itis also illustrated that the support surface 4k' has an angular value"c" which corresponds precisely to the angular value of the rod. Alsoshown in FIG. 3, in full lines, is a position in which the rod has beenmoved axially towards the needle 3 through a small distance, therewithrotating the support surface 5k out of coaction with the support surface4k.

The support surface 5k' has been rotated into sliding coaction with thesurface 4k' and the piston 4 is urged downwardly while the rod rotatesthe section 5a' out of engagement with the groove.

In the full line position shown in FIG. 3, the piston 4 can again bemoved by the rod 5 away from the needle 3, through the contact surfaceafforded by the support surfaces 5k and 4k. A further, small movementtowards the needle 3, however, will cause the support surface 5k to moveout of contact with the surface 4k causing further movement of the rod 5away from the needle 3 and thereby causing the rod terminating section5a' to leave its position of coaction with the piston 4 and the piston 4will thus be pressed solely in one single direction, namely towards theneedle (3).

Upon completion of an injection with the piston 4 located nearest theneedle, the syringe can thus again become the subject for a newinjection.

As illustrated in FIGS. 3 and 4, the piston 4 is provided peripherallywith diametrically positioned projections 4r and 4s, or wall parts, anda web 4u which is intended to support a sealing ring (not shown) forsealing coaction with the container 2.

The projection 4r is provided with a recess or a groove forming supportsurfaces 4k and 4k' and the projection 4s is provided with acorresponding, but turned, recess or groove forming support surfaces 4mand 4m'.

FIG. 5 illustrates a sequence A-E of positions taken by the piston andthe rod connecting and disconnecting means during part of a cycle, withthe tolerances being exaggerated for the purpose of illustration.

The sequence A is intended to show that when acted upon by a force inthe direction of the arrow P1, the rod terminating section 5a' causesthe piston to accompany movement in the direction of the arrow R1, andthat the angular value of the surface 4k is selected so that the rodterminating part 5a' will be located at the bottom of the groove.

The sequence B is intended to show that when the rod terminating section5a' is urged in the direction of the arrow P2, it will lie against thesurface 4k' and when displaced in the direction of the arrow S2, thepiston 4 will move downwards, without rotating.

When the rod terminating section 5a' is in the position shown insequence C, the rod 5 can be moved in the opposite direction, accordingto the arrow P1, sequence D being intended to illustrate this movement.

This movement presses the surface 5k against the surface 4k and inresponse to movement in the direction of the arrow s1, the piston 4 willmove upwards, without rotating. In an aspiration cycle, piston and rodare turned upside down.

FIG. 4 is a partial cross-sectional view taken through projection 4s anddirected toward the needle 3.

When the rod terminal section 5a' is moved to the position shown insequence E, said section will have moved out of coaction with thegroove, with the surfaces 4k and 4k', and the piston 4 can only be movedtowards the needle by the rod 5.

FIG. 6 illustrates in perspective the respective piston and rodconnecting and disconnecting means in a position where they are not inengagement with one another and the rod 5 is only able to urge thepiston 4 towards the needle.

The illustrated rod has a Z-shaped cross-section, presenting a broadcentral part 5p and two mutually opposed edges 5s and 5r, according toFIG. 7A of similar cross-section.

Within the framework of the same material consumption, and possibly lessmaterial consumption, it is possible to make the central part 5p'thinner and the edges 5s' and 5r' longer and even thicker than thecentral part shown in FIG. 7B.

FIG. 7C illustrates a V-shaped or a L-shaped cross-section, with theparts 5t and 5t' forming a right angle and having a similarcross-section.

It lies within the scope of the invention to manufacture rod 5 in atwo-part die while obtaining sufficient resistance to bending about abending line with least bending resistance, such as the bending line 5yin FIG. 7B, for a given application. It will be understood that aselected cross-section will also afford other cross-sectional shapes andother mass distributions than those illustrated in FIGS. 7A, 7B and 7C.

The invention is not restricted to the aforedescribed and illustratedexemplifying embodiment thereof, since modifications and changes can bemade within the scope of the inventive concept as defined in thefollowing claims.

We claim:
 1. A syringe comprising a container a rod which can be movedreciprocatingly relative to said container, one end of which containerforming means to coact with a needle, and a piston which coacts with therod, said rod comprising:means for connecting and disconnecting thepiston to and from the rod; said connecting and disconnecting meansincluding a T-shaped bar having piston support surfaces facing toward apiston end of the rod; said piston support surfaces extend substantiallyperpendicular to a center line on the rod and are inclined in adirection of rotational movement relative to said center line of therod; said piston support surfaces arranged so as to coact with similarlyangled support surfaces on the piston; wherein said connecting anddisconnecting means are brought to a connecting position relative tosaid piston when the piston is drawn by the rod away from the needle,and are brought to a disconnecting position relative to said piston whenthe piston is urged by the rod in a direction towards the needle; andsaid syringe further including means for the rod to coact with thecontainer in a manner such that when the rod is moved axially inrelation to the container the rod is rotated through an angle about saidcenter line in relation to said container.
 2. The syringe of claim 1,wherein said piston support surfaces are inclined in a direction ofmovement of the rod at an angle of less than 25°.
 3. The syringe ofclaim 1, wherein said piston support surfaces are inclined in adirection of movement of the rod at an angle of 5°-15°.
 4. The syringeof claim 1, wherein said piston support surfaces are comprised of twosurfaces, said T-shaped bar further including two surfaces facing awayfrom said piston end of the rod.
 5. The syringe of claim 1, wherein saidrod has an angular cross section, a broad central thin part, andstiffening edges which extend from said broad central thin part.
 6. Apiston for forming part of a syringe, said syringe including a containerand a rod which rod can be moved reciprocatingly relative to saidcontainer, one end of which container forms a means to coact with aneedle, said piston for coacting with the rod, said pistoncomprising:means for connecting and disconnecting the piston to and fromthe rod; said connecting and disconnecting means including oppositeperipheral projections having rod support surfaces facing toward a rodend of the piston; said rod support surfaces extending substantiallyperpendicular to a center line on the piston and are inclined in adirection of rotational movement relative to said center line of thepiston; said rod support surfaces arranged so as to coact with similarlyangled support surfaces on the rod; wherein said connecting anddisconnecting means are brought to a connecting position relative tosaid rod when the piston is drawn by the rod away from the needle, andare brought to a disconnecting position relative to said rod when thepiston is urged by the rod in a direction towards the needle.
 7. The rodof claim 6, wherein said piston support surfaces are inclined in adirection of movement of the rod at an angle of less than 25°.
 8. Therod of claim 6, wherein said piston support surfaces are inclined in adirection of movement of the rod at an angle of 5°-15°.
 9. The rod ofclaim 6, wherein said piston support surfaces are comprised of twosurfaces, said opposite peripheral projections further including twosurfaces facing away from a rod end of the piston.
 10. The piston ofclaim 6, wherein said rod has an angular cross section, a broad centralthin part, and stiffening edges which extend from said broad centralthin part.